In the oil and gas industry, rig up of pressure control equipment requires pressure testing of the equipment to ensure they will hold the well pressure. For example, in wireline logging or workover operations, whenever a wireline lubricator stack is rigged up, it has to be pressure tested before it can be used for deploying a toolstring inside the well. During these operations, especially during workover operations such as bailing, the toolstring may have to be taken apart many times to service the bailer, which requires pressure testing of the lubricator every time.
Fluids and especially compressed gas, such as air, trapped inside pressure control equipment (PCE) can store and release more energy than a liquid held at the same pressure and so may become a safety hazard if not handled properly. For this reason, pressure control equipment should be vented to release all trapped gas and other fluids trapped, prior to testing the PCE at full test pressure. Also, during rig down, pressure control equipment should be vented to release any trapped fluids or gases trapped, prior to disassembly. This measure prevents exposure of operators to hazardous well fluids. For example, after a wireline logging or workover operation, the lubricator stack should also be vented to release any gases or fluids before disconnecting the lubricator.
Releasing fluid or gas from pressure control equipment can typically be a rather cumbersome and risky operation. For example, it is not unusual for a wireline lubricator stack to be in excess of 12 meters high. Venting the trapped gas prior to full pressure testing, should be performed from the highest point of the lubricator stack.
Typically, in order to discharge any fluid and gas from a lubricator stack, an operator may loosen a connection between two lubricator sections or may open an existing valve slightly to allow venting to take place. This operation must be performed as close to the top of the lubricator as possible. Moreover, the safety of the operation is dependent on the knowledge and skill of operators to ensure that venting is not performed when there is an excessively high pressure in the lubricator. If it transpires that the pressure of the trapped fluids or gases is higher than the operator thinks it is, the operator may be exposed to serious risk.